Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$80.50	11.345%	$89.6327	$89.63	$89.65	$89.60
Purchase #2	$119.75	3.523%	$123.9688	$123.97	$123.95	$124.00
Purchase #3	$119.39	10.492%	$131.9164	$131.92	$131.90	$131.90
Purchase #4	$135.68	7.860%	$146.3444	$146.34	$146.35	$146.30
Purchase #5	$49.90	7.769%	$53.7767	$53.78	$53.80	$53.80
Purchase #6	$77.99	6.655%	$83.1802	$83.18	$83.20	$83.20
Purchase #7	$145.84	12.523%	$164.1035	$164.10	$164.10	$164.10
7 purchase totals =	$729.05		$792.9227	$792.92	$792.95	$792.90